1. Field of the Invention
The present invention relates to a clamping method of an injection and compression molding machine, comprising the steps of temporarily stopping a movable mold at a pre-clamping position located before a final clamping position and performing high-pressure clamping in accordance with the filling of resin.
2. Description of the Relevant Art
An injection and compression molding machine is known wherein the injection and compression molding machine normally performs clamping as shown in FIG. 4. First, a movable mold is moved forward from a mold opening position to a preset slowdown start position at a high speed (step S21). When the mold reaches the slowdown start position, it is moved to the pre-clamping position located before the final clamping position while slowly decreasing the speed (steps S22 and S23). When the movable mold reaches the pre-clamping position, it is stopped to start injection and filling of the resin under an above state (steps S24, S25, S26, and S27). Then, the movable mold is moved up to the final clamping position during or after injection and filling of resin to perform high-pressure clamping (step S28). Thereafter, mold opening including a cooling process is performed (step S29). Because this type of the injection and compression molding machine slightly opens the mold at the time of injection and filling of resin, it has advantages wherein the release of gas from the mold is accelerated and the flowability of resin is improved. Moreover, because the machine performs high-pressure clamping, it has an advantage wherein the transfer property of resin to the mold is improved.
For an injection and compression molding machine, it is important to accurately move a movable mold up to a pre-clamping position in order to improve the molding quality. inaccurate setting of the pre-clamping position would cause an imperfect molding due to insufficient or excessive filling of the resin.
Therefore, a movable mold has been moved from a mold opening position to a preset pre-clamping position by using a high-accuracy linear scale disclosed in the official gazette of Japanese Patent Publication No. 63(1988)-9247 and thereby accurately detecting a moving position of the movable mold so far.
However, though an existing clamping method makes it possible to accurately move a movable mold from a mold opening position to a pre-clamping position, it has problems wherein an accurate position is not always set when viewed from a fixed mold and the weight of a molded part, the amount of gas to be released, and the transfer property are not stabilized because of various error factors such as deformation of a tie bar for movably supporting the movable mold due to heat or tension, clearance of a mechanical structure, and setting error of a position detector such as a linear scale.